Field of the Invention
The present invention relates to an electronic device that accommodates an electronic element in a package, and a method of manufacturing an electronic device.
Background Art
Hitherto, surface-mounted electronic devices have generally been used for mobile phone and mobile information terminals. Meanwhile, in crystal vibrators, micro electro mechanical systems (MEMS), gyroscopes, acceleration sensors, and the like, a hollow cavity is formed inside a package, and an electronic element such as a crystal vibrator and a MEMS is enclosed in the cavity. A glass material is used as the package. For example, the electronic element is mounted on a base substrate, and a glass lid is bonded thereto by anodic bonding, thereby sealing the electronic element. Anodic bonding between glass materials has the advantages of high air tightness and low costs (JP-A-2011-155506).
FIG. 6 is a cross-sectional view of this type of electronic device (FIG. 1 of JP-A-2011-155506). An electronic device 101 includes a base 110, an electronic component 140 mounted on the base 110, and a cap 150 which accommodates the electronic component 140 and is bonded to the base 110. The base 110 is provided with a through electrode 121 passing through the base in a through-thickness direction, a first metal film 122 which is electrically connected to the through electrode 121, and a circuit pattern 130 and a second metal film 123 which electrically connect the through electrode 121 and the electronic component 140 to each other. An external electrode 160 formed of a metal film is formed outside the first metal film 122.
Here, a nickel-iron alloy is used as the through electrode 121. Gold formed by an electroless plating method is used as the first metal film 122. In addition, a low melting point glass, not shown in the drawing, is used between the through electrode 121 and base 110 to improve air tightness by thermal welding.
In this type of electronic device, a nickel-iron alloy is used as the through electrode 121, and a gold thin film is used as the first metal film 122 for preventing the through electrode 121 from oxidizing. Further, the external electrode 160 is mostly formed of a conductive adhesive such as a conductive paste. When the external electrode 160 is formed of a conductive adhesive such as a silver paste, it is difficult to completely block moisture due to an insufficient humidity resistance of the conductive paste. There is a great difference in ionization tendency between a nickel-iron alloy and gold. Accordingly, when moisture and the like are attached between the through electrode 121 and the first metal film 122, the through electrode 121 corrodes due to a battery effect, which causes a decrease in conductivity. In addition, a low melting point glass is used between the through electrode 121 and the base 110, and a gold thin film of the first metal film 122 is formed on an end face of the through electrode 121 by an electroless plating method. Since a gold thin film is not likely to be formed in the low melting point glass by an electroless plating method, a boundary portion between the through electrode 121 and the first metal film 122 is exposed, and thus there is a tendency for corrosion to progress.